Concealed windshield broadband antenna

ABSTRACT

An AM-FM antenna for vehicular radio receivers comprising a pair of L-shaped fine wire conductors disposed between the laminates of a windshield in reversely symmetrical relation and connected to a receiver by way of a coaxial lead. Spacings between the conductors and the vehicle body portion bounding the windshield are chosen to capacitively load the antenna for AM reception and to resonate the antenna for FM reception.

United States Patent William K. Jensen Royal Oak, Mich.

Oct. 31, 1968 Apr. 27, 1971 General Motors Corporation Detroit, Mich.

Inventor Appl. No. Filed Patented Assignee CONCEALED WINDSHIELDBROADBAND ANTENNA 6 Claims, 2 Drawing Figs.

u.s. Cl 343/712, 343/830, 343/873 Int. Cl H0lq 1/32 Field of Search343/705,

[56] References Cited UNITED STATES PATENTS 3,414,902 12/1968 Shaw343/713 FOREIGN PATENTS 647,665 12/1950 Great Britain 343/705 PrimaryExaminer-Eli Leberman Attorneys-E. W. Christen, G. R. Meland and AlbertF. Duke ABSTRACT: An AM-FM antenna for vehicular radio receiverscomprising a pair of L-shaped fine wire conductors disposed between thelaminates of a windshield in reversely symmetrical relation andconnected to a receiver by way of a coaxial lead. Spacings between theconductors and the vehicle body portion bounding the windshield arechosen to capacitively load the antenna for AM reception and to resonatethe antenna for FM reception.

CONCEALED WINDSHIELD BROADBAND ANTENNA INTRODUCTION AND SUMMARY OF THEINVENTION This invention relates to antennae for vehicular radioreceivers and more particularly to a broadband antenna which includesconductors disposed within a vehicle window opening such as thewindshield aperture.

In accordance with the present invention a highly inconspicuous antennafor vehicle radio receivers is provided. This is accomplished by placingconductors such as fine wires within a window opening in the vehiclebody. So disposed, the conductors may be supported by the glass in thewindow. In a specific and preferred embodiment, the conductors areplaced in the windshield aperture between the glass laminates so as tobe fully supported in a fixed position relative to the body.

The present invention also provides an antenna of a configuration whichexhibits broadband reception characteristics so as to accommodate bothAM and FM signal reception. In general, this is accomplished through theuse of two separate conductors of reversely symmetrical disposition eachof which includes a portion which is relatively close to a metallic bodyelement and a portion which is relatively remote from the metallic body.The conductor portions which are relatively remote from the bodyintercept the incident radio waves and the conductor portions which arerelatively close to the body act to condition the antenna for broadbandreception. In the AM band, the conductor portions relatively close tothe body form capacitor elements which load the remote portions forproper antenna impedance characteristics. In the FM band, the relativelyclose conductor portions act to resonate the antenna conductors formaximum response in the standard FM frequency band.

Further features and advantages of the invention will become apparentupon reading the following specification which is to be taken with theaccompanying drawings of which:

FIG'. 1 is a plan view of a vehicle windshield incorporating anembodiment of the present invention; and

FIG. 2 is a bottom view of the vehicle windshield showing more of thenature of the connection means.

In FIG. 1, the illustrative embodiment of the antenna comprises a pairof L-shaped fine wire conductors 10 and 12 having terminal ends andbeing disposed in reversely symmetrical fashion within a vehiclewindshield aperture defined by a surrounding metallic body molding 14.While the molding 14 is shown as one piece, it may also consist ofseveral connected sections. Conductors l and 12 are supported in theposition shown by the windshield glass 16. This may be accomplished byplacing the conductors l0 and 12 in the thermoplastic layer 18 betweenlaminates 20 and 22 shown in FIG. 2. Alternatively, the conductors maybe disposed on the surface of glass 16 by means of a transparent plastictape.

As shown in FIG. 1 with reference to conductor 10, each of the reverselysymmetrical conductors and 12 includes a transverse portion A which isrelatively closely adjacent the body molding 14. Each conductor alsoincludes a longitudinal portion B which is near the centerline ofwindshield glass 16 and thus is relatively remote from the body molding14.

The longitudinal portions B of conductors l0 and 12 extend in parallelfashion to a point in the bottom center of the windshield glass'16. Atthis point conductors l0 and 12 are electrically connected to acopperfoil contact 24. As shown in the FIGS., contact 24 extends between thelaminates and 22 to the bottom periphery where it wraps around theinterior laminate 20.

The antenna comprising conductors l0 and 12 is connected to a radioreceiver 26 by means of a coaxial conductor cable 28. The centerconductor of cable 28 is connected by a short lead 30 to the foilcontact 24. The outerconductor of cable 28 is connected to the bodymolding 14 by a conductor represented at 32. The body molding 14 isgrounded as indicated at 34.

It will be understood that receiver 26 may be equipped for either AM orFM broadcast reception or, alternatively, it may be equipped for both AMand FM reception as is often the case. The antenna represented byconductors 10 and 12 in the windshield aperture defined by molding 14 iseffective to abstract energy from passing radio waves in both AM and FMfrequency bands. Accordingly, the antenna is particularly suitable forbroadband applications.

In the AM band of 550 to 1,600 kc., the conductors 10 and 12 constitutea capacitively loaded, two-conductor antenna. To abstract maximum energyfrom a passing AM frequency radio wave, it is desirable to match thereactance of the load with a reactive component of antenna impedance ofopposite type or sign. The transverse conductor portions A of conductors10 and 12 are capacitively coupled to the adjacent grounded body molding14. Accordingly, the capacitances produced by the transverse portionsare in series with the longitudinal conductor portions B and serve to atleast approximate the desired reactance match. It has been found thatwith the antenna conductor disposed within the laminates 20 and 22, asatisfactory capacitance value of more than 40 pf. can be achieved at900 kc. Of course, it will be understood that wire size, length andspacing may affect this value, as well as the dielectric constant of thematerial between the.

conductors 10 and 12 and the body molding 14.

For FM broadcast reception, the transverse portions A adjacent bodymolding 14 may be considered to function as an open wire transmissionline having,distributed inductive and capacitive impedancecharacteristics. The longitudinal portions B again act as a shortvertical antenna. Like all transmission lines, the conductors l0 and 12act as a resonant circuit. Antenna resonance occurs when the opencircuit impedance of the top sections formed by transverse portions Aand the reactance of the longitudinal portions B cause zero totalreactance. It has been found that by proper choice of wire size, lengthand spacing, this resonant circuit may be made resistive, that is,resonant, at approximately the center of the FM band, mc. Thus theantenna presents a relatively constant impedance to the receiver 26 overthe FM band.

Although not to be understood as limiting the present invention, thefollowing design parameter numbers have been found to give goodperformance in both the AM and FM bands:

Wire diameter in.0. 003 Transverse conductor length in.22. 5Longitudinal conductor length in.20. 0 Transverse conductor spacing tobody molding in.-1 Spacing between longitudinal portions in.0. 5 Antennacapacitance pf.40. 8 Open circuit transmission line impedance 1 210 1Ohms at 100 me.

The transverse conductor portions A may be of the same length asindicated above to produce a purely resistive, or resonant, condition ata frequency at or approximately at the center of the FM band.Alternatively, the portions A may be made of dissimilar length ordissimilar spacing relative to the molding 14. Changes in the conductorlength and spacing result in changes in the distributed impedancequantities and thus alter the resonant frequency. Since the conductors10 and 12 are physically separate, it is possible to resonate oneconductor at a frequency of less than 100 mc. and the other conductor ata frequency of more than 100 mc. For example, resonant frequencies of 92mc. and 108 mc. are obtainable with changes in conductor length of 10percent or less.

' it has been found that a change in the spacing between conductorportions A and the body molding 14 produces a less proportional shift inresonance than does a change in wire length. Accordingly, it mayordinarily be preferable to vary antenna characteristics by changingconductor length where such change is desired.

It has also been found that the window opening defined by body molding14 exhibits a resonant cavity characteristic which results in antennasensitivity to signals of frequencies in bands other than AM and FM. Forexample, the combination of the'conductors l and 12 in a typicalwindshield opening exhibits a resonance at approximately 27 me. which iswithin the Citizens Band. Accordingly, the antenna may also serveadditional special purpose receivers.

It is to be understood that the foregoing description refers to anillustrative embodiment of the invention and is not to be construed in alimiting sense.

I claim:

1. An AM-FM broadband radio antenna for a vehiclemounted receivercomprising in combination: a metallic vehicle body element defining awindow opening, a window disposed in the opening, first and secondconductorshaving terminal ends, the conductors being disposed in theopening in reversely symmetrical relation and supported by the window,each of the conductors having a portion relatively closely adjacent butspaced from the metallic body element and a portion relatively remotefrom the metallic body element, the relatively remote portions servingto develop electrical radio signals in response to interceptedelectromagnetic radio waves, the relatively adjacent portions providinga capacitance determined as a function of the length of the relativelyadjacent portions and as a function of the spacing of the relativelyadjacent portions from the metallic body element, the capacitance havingsuch a value that the relatively adjacent portions serve to tune therelatively remote portions for maximum performance in both the AM bandand the'FM band, and meanselectrically connecting the terminal ends ofthe remote conductor portions and the body element to a receiver in thevehicle.

2. An AM-FM broadband radio antenna for a vehiclemounted receivercomprising in combination: a metallic vehicle body element defining awindshield opening, a

windshield disposed in the opening, 'first and second conductors havingterminal ends, the conductors being disposed in the opening in reverselysymmetrical relation and supported by the windshield, each of theconductors having a first portion'extending transversely of thewindshield and relatively closely adjacent but spaced from the bodyelement and a second portion extending longitudinally of the windshieldand relatively remote from the metallic body element, the secondconductor portions serving to develop electrical radio signals inresponse to intercepted electromagnetic radio waves, the first conductorportions providing a distributed inductance and a distributedcapacitance, the distributed inductance determined as a function of thelength of the first conductor portions, the distributed capacitancedetermined as a function of the length of the first conductor portionsand as a function of the spacing of the first conductor portions fromthe metallic body element, the distributed inductance and thedistributed capacitance having such values that the first conductorportions serve to tune the second conductor portions for properimpedance matching in the AM band and for maximum resonant response inthe FM band, contact means electrically connecting the terminal ends ofthe second portions, and means electrically connecting the contact meansand the body element to a receiver in the vehicle.

3. A broadband radio antenna for a vehicle-mounted receiver comprisingin combination: a windshield aperture in the vehicle defined by ametallic body element, a laminated windshield of known dielectricconstant disposed within the aperture, first and second conductorsdisposed between the laminates of the windshield, and havin transverseortions adjacent but spaced from e body e ement boun mg the upperperiphery of the windshield and longitudinal portions extending inspaced parallel fashion along the centerline of the windshield, anantenna lead comprising coaxial center and outer conductors forconnecting the first and second conductors to a radio receiver, meansadjacent the bottom periphery of the windshield for electricallyconnecting the longitudinal portions of the first and second conductorsto the center conductor, means connecting the body element to the outerconductor, the first and second conductors being constructed andarranged to operate as a'capacitively loaded dipole antenna in the AMband and a resonant antenna in the FM band.

4. A broadband radio antenna as defined in claim 3 wherein thetransverse portions are of effectively dissimilar length to resonate theantenna at spaced frequencies in the FM band.

5. An AM-FM antenna for vehicular radio receivers comprising incombination: a windshield aperture defined by a metallic vehicle bodyelement, a laminated windshield of known dielectric constant disposedwithin the aperture, first and second L-shaped fine wire conductorsdisposed between the laminates of the windshield in reverselysymmetrical relation, each of the conductors having a transverse portionadjacent but spaced from the body element bounding the top periphery ofthe windshield, and a longitudinal portion extending in spaced parallelfashion along the centerline of the windshield to points adjacent thebottom periphery thereof, an antenna lead comprising coaxial center andouter conductors for connecting the first and second conductors to aradio receiver, means connecting the first and second conductors to thecenter conductor at said points, and means connecting the body elementto the outer conductor, the first and second conductors beingconstructed and arranged such that in the AM band the transverseportions operate as capacitors loading the longitudinal portions, and inthe FM band the transverse portions operate as a transmission line withthe adjacent body element to resonate the conductors.

6.'A broadband radio antenna as defined in claim 5 wherein thetransverse portions are of dissimilar length to resonate the first andsecond conductors at spaced frequencies in the FM band.

1. An AM-FM broadband radio antenna for a vehicle-mounted receivercomprising in combination: a metallic vehicle body element defining awindow opening, a window disposed in the opening, first and secondconductors having terminal ends, the conductors being disposed in theopening in reversely symmetrical relation and supported by the window,each of the conductors having a portion relatively closely adjacent butspaced from the metallic body element and a portion relatively remotefrom the metallic body element, the relatively remote portions servingto develop electrical radio signals in response to interceptedelectromagnetic radio waves, the relatively adjacent portions providinga capacitance determined as a function of the length of the relativelyadjacent portions and as a function of the spacing of the relativelyadjacent portions from the metallic body element, the capacitance havingsuch a value that the relatively adjacent portions serve to tune therelatively remote portions for maximum performance in both the AM bandand the FM band, and means electrically connecting the terminal ends ofthe remote conductor portions and the body element to a receiver in thevehicle.
 2. An AM-FM broadband radio antenna for a vehicle-mountedreceiver comprising in combination: a metallic vehicle body elementdefining a windshield opening, a windshield disposed in the opening,first and second conductors having terminal ends, the conductors beingdisposed in the opening in reversely symmetrical relation and supportedby the windshield, each of the conductors having a first portionextending transversely of the windshield and relatively closely adjacentbut spaced from the body element and a second portion extendinglongitudinally of the windshield and relatively remote from the metallicbody element, the second conductor portions serving to developelectrical radio signals in response to intercepted electromagneticradio waves, the first conductor portions providing a distributedinductance and a distributed capacitance, the distributed inductancedetermined as a function of the length of the first conductor portions,the distributed capacitance determined as a function of the length ofthe first conductor portions and as a function of the spacing of thefirst conductor portions from the metallic body element, the distributedinductance and the distributed capacitance having such values that thefirst conductor portions serve to tune the second conductor portions forproper impedance matching in the AM band and for maximum resonantresponse in the FM band, contact means electrically connecting theterminal ends of the second portions, and means electrically connectingthe contact means and the body element to a receiver in the vehicle. 3.A broadband radio antenna for a vehicle-mounted receiver comprising incombination: a windshield aperture in the vehicle defined by a metallicbody element, a laminated windshield of known dielectric constantdisposed within the aperture, first and second conductors disposedbetween the laminates of the windshield, and having transverse portionsadjacent but spaced from the body element bounding the upper peripheryof the windshield and longitudinal portions extending in spaced parallelfashion along the centerline of the windshield, an antenna leadcomprising coaxial center and outer conductors for connecting the firstand second conductors to a radio receiver, means adjacent the bottomperiphery of the windshield for electrically connecting the longitudinalportions of the first and second conductors to the center conductor,means connecting the body element to the outer conductor, the first andsecond conductors being constructed and arranged to operate as acapacitively loaded dipole antenna in the AM band and a resonant antennain the FM band.
 4. A broadband radio antenna as defined in claim 3wherein the transverse portions are of effectively dissimilar length toresonate the antenna at spaced frequencies in the FM band.
 5. An AM-FMantenna for vehicular radio receivers comprising in combination: awindshield aperture defined by a metallic vehicle body element, alaminated windshield of known dielectric constant diaposed within theaperture, first and second L-shaped fine wire conductors disposedbetween the laminates of the windshield in reversely symmetricalrelation, each of the conductors having a transverse portion adjacentbut spaced from the body element bounding the top periphery of thewindshield, and a longitudinal portion extending in spaced parallelfashion along the centerline of the windshield to points adjacent thebottom periphery thereof, an antenna lead comprising coaxial center andouter conductors for connecting the first and second conductors to aradio receiver, means connecting the first and second conductors to thecenter conductor at said points, and means connecting the body elementto the outer conductor, the first and second conductors beingconstructed and arranged such that in the AM band the transverseportions operate as capacitors loading the longitudinal portions, and inthe FM band the transverse portions operate as a transmission line withthe adjacent body element to resonate the conductors.
 6. A broadbandradio antenna as defined in claim 5 wherein the transverse portions areof dissimilar length to resonate the first and second conductors atspaced frequencies in the FM band.